Currently marketed tires are made from raw materials derived from petroleum resources such that these raw materials account for half or more of the total weight of the tire. For example, common radial tires for passenger cars contain, based on the total weight of the tire, about 20% of synthetic rubber and about 20% of carbon black as well as aromatic oil and synthetic fibers. Thus, they contain at least 50% of petroleum-derived raw materials as a whole.
The recent emphasis on the environmental issues, however, has led to tighter CO2 emission restrictions. Moreover, since the petroleum raw material is a limited resource and the amount of the material supplied is decreasing year by year, oil prices are expected to escalate in the future and thus the use of petroleum-derived raw materials has a limit.
Hence, the people's desire to construct a sound material-cycle society has recently become stronger. Accordingly, there is a need for a departure from fossil fuel dependence in the material field as well as in the energy field, and the use of biomass has been focused on.
For example, Patent Literature 1 discloses an environment-friendly tire technology to prepare for a future decrease in petroleum supply. In this technology, a tire is formed in which 75% by weight or more of the total weight of the tire is made from raw materials derived from resources other than petroleum, for example, by replacing synthetic rubber with natural rubber, carbon black with inorganic filler or bio filler, petroleum oil with vegetable oil or fat, and synthetic fibers with natural fibers.
However, unfortunately, natural rubber is inferior in fuel efficiency, wet grip performance, and processability (particularly, wet grip performance and processability) to synthetic rubber such as styrene-butadiene rubber (SBR).